On the way to further exploit offshore wind energy, conventional fixed-bottom technology has been limited by the water depth. After the worlds first full scale floating wind turbine being installed in the North Sea in 2009, the floating support structure for offshore wind turbines is most likely becoming not only a technically feasible but also an economically viable solution, especially for regions of water depth over 50 meters. However, less attentions have been paid on floating support strucure, which is a very important part. Derived from commercialized offshore oil and gas platform of cell spar, a conceptual design of a cell-spar-buoy support structure for NREL 5 MW offshore wind turbine is proposed. In this system, structural type of cells is absorbed for cost reduction while damping configurations are used to optimize the stability of wind turbine. For further hydrodynamic performance estimations, numerical simulations have been performed to compute the response amplitude operators (RAOs) and the wave response motions, which are the key factors of the preliminary design. Meanwhile, the motion performance of the platform with mooring system in operating conditions and mooring line tensions under the 50 years return period storm survival condition in the South China Sea was calculated in time domain. The results showing excellent motion performance of cell-spar-buoy.